I wish I could tell you there is a really easy way but there isn't. Going on JobSlinger would give you an idea of which companies have jobs in your area. By time time you see the postings on JobSlinger, the jobs are long gone, so you won't get actual jobs from JobSlinger. But it would tell you which companies are posting assignments in your area and you could then sign up with those companies and be ready when they post more jobs.
If you have signed up with 20 companies in only one week and already found work with 5 of them, you're not doing bad. That 25% of the companies you have applied with. And, if you have only been doing it a week, some of the other 15 may actually have work in your area but it may have not been posted within the week. A lot of companies only post their assignments once a month and their job boards stay empty for a lot of the month. You may get e-mails in a week or two from some of the others as they post later in the month.
Try to speed up the application process as much as you can. Except for the companies requiring tests (and you can postpone taking the tests with most companies), there are usually only two narrative questions: one is usually a short one-paragraph job history and the other is a sample narrative of your best (or worst) restaurant or retail experience. Type both of those in a Word document and save them. You can use the same ones for most of your applications. Some browsers will auto-fill your personal information - FireFox and Chrome both do for me - or download RoboForm. You can shorten the process of registering with a new company to almost nothing.